Geodesic
A note on extreme points in the closed unit ball of upper triangular 2 × 2 matrices over a C * -algebra
Filomat, Tome 36 (2022) no. 19, p. 6767

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DOI

Given a unital C *-algebra A, let M m×n (A) be the set of all m×n matrices algebra over A and M n (A) 1 be the closed unit ball of M n×n (A). Let x = a b 0 c ∈ M m+n (A) 1 be determined by a ∈ M m×m (A), b ∈ M m×n (A) and c ∈ M n×n (A). Some characterizations are given such that the above upper triangular matrix x is an extreme point of M m+n (A) 1 and X m,n (A) respectively, where X m,n (A) is the subset of M m+n (A) 1 consisting of all upper triangular matrices.
DOI : 10.2298/FIL2219767T
Classification : 46L05, 47L07
Keywords: C∗-algebra, upper triangular matrix, extreme point 
Xiaoyi Tian; Qingxiang Xu. A note on extreme points in the closed unit ball of upper triangular 2 × 2 matrices over a C * -algebra. Filomat, Tome 36 (2022) no. 19, p. 6767 . doi: 10.2298/FIL2219767T
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     author = {Xiaoyi Tian and Qingxiang Xu},
     title = {A note on extreme points in the closed unit ball of upper triangular 2 {\texttimes} 2 matrices over a {C} * -algebra},
     journal = {Filomat},
     pages = {6767 },
     year = {2022},
     volume = {36},
     number = {19},
     doi = {10.2298/FIL2219767T},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.2298/FIL2219767T/}
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